The present invention relates to the field of remote powering, and more particularly to a means for power management of rack mounted remote powering systems having a plurality of shared power sources.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to; reduced cost of installation; centralized power and power backup; and centralized security and management.
Several patents addressed to this issue exist including: U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference and U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference. Furthermore a standard addressed to the issue of powering remote devices over an Ethernet based network, known as Power over Ethernet (PoE), has been published as IEEE 802.3af-2003, whose contents are incorporated herein by reference.
PoE is typically a scalable technology, in which an initial installation may supply power functionality to a limited number of ports in the system. Over time, additional ports may require power, with a resultant need for additional sources of power. Each port supplies power to a connected powered device (PD), with power being transmitted from the port to the PD over the structured communication cabling. For each group of ports to be powered, a PoE managing circuit is provided to accomplish detection, optional classification, powering and monitoring in accordance with the above standard. In order to ensure an orderly turn on of multiple ports, and to enable management and control of ports in the event that the demand for power by ports exceeds the power available, ports are assigned priorities. In one embodiment, priorities are assigned based on physical port numbers. In another embodiment, priorities are user settable, preferably in levels. In an exemplary embodiment 3 user settable levels are available for each port. Ports of like priority level are then further prioritized by physical port number.
PoE devices such as PoE enabled switches, PoE midspans and PoE enabled patch panels typically comprise, or have associated therewith, a plurality of PoE managing circuits. A single device may provide power to 1, 6, 12, 24 or 48 ports or any other number of ports. Some ports may have PDs attached thereto, whereas other ports may not. In an exemplary embodiment, a switch supporting 48 ports may comprise 4 PoE managing circuits, each of the PoE managing circuits controlling power for up to 12 ports.
As indicated above, as additional PDs to be powered are added the required power may begin to meet or exceed the initially supplied power. One well developed method of adding additional power to a system is the use of a plurality of power sources, or power banks, which are connected together in a power sharing arrangement.
A major difficulty in the use of a plurality of power sources is the action that must be taken in the event of a failure, or reduced output, of one of the plurality of power sources. For example, in a network in which power over Ethernet is supplied to a large number of PDs, groups of PDs receive their power from one of a plurality of PoE managing circuits each of which obtains power from the plurality of power sources. In the event of a failure of one of the plurality of power sources powering the plurality of PoE managing circuits, some ports of selected PoE managing circuits supplying power to some PDs must be disabled so as to avoid an excess load on the remaining power sources which may result in overall system failure or shut down. Furthermore, the PDs which are not to be disabled are preferably to be shielded from any adverse effect from the failed power source. This requires rapid action in the case of power source failure, preferably by disabling or reducing power drawn by sufficient ports, so as to reduce the total power drawn within a short time period, such as 20 milliseconds, or more preferably 2 milliseconds. Disabling or reducing power drawn by sufficient ports prevents an overload condition on the remaining power sources. It is to be understood that shutting down power to a port is herein used interchangeably with disabling a PD, since each PD is connected to, and receives power from, a specific port.
Furthermore, at start up or upon the addition of a power source to the plurality of power sources, a large number of ports may be potentially powerable. In prior art systems, the PoE devices are typically responsive to a host controller which sends power enabling commands to enable all port of the PoE device. Alternatively, the host controller may enable specific ports of the PoE device. The term enabling as used herein means authorizing the powering of a connected port, in the event that the PoE managing circuit detects that a valid PD is attached thereto. In one embodiment the enabling is done responsive to detection and optional classification, and in another embodiment the enabling is done prior to detection and optional classification. In the event that a port has not been enabled, detection and optional classification may be accomplished however subsequent powering is not accomplished.
In the event that a plurality of PoE devices are connected, each of the plurality of PoE devices having attached thereto a number of PDs requiring powering, the amount of power required to power all of the attached PD may exceed that power available. Furthermore, upon initial powering of a PD, an inrush current which is in excess of the normal operating current is typically observed. One solution is to enable all the attached PoE devices, unfortunately this will result in a power demand exceeding total available power, resulting in early power supply failure or unreliable powering of at least one port. This problem is further exacerbated by the inrush current. Furthermore, global priority is not maintained, as individual PoE devices may power according to priority, however priority across PoE devices is not adhered to. This may result in low priority ports attached to a first PoE device being powered, while a high priority port attached to a second PoE device is not powered.
Another solution is for the host controller to individual enable ports, the host controller awaiting confirmation of powering responsive to an initial command before enabling additional ports. Unfortunately this is very time consuming, and for very large systems results in unacceptable delays. In one non-limiting example of such a sequential powering method, in which enabling detection, classification, powering and reporting a specific port occupies a 1 second cycle time, enabling 1,000 ports requires in excess of 15 minutes.
What is therefore needed, and not known in the prior art, is a method for rapidly enabling powering of ports suitable for use in a large system having a plurality of PoE devices, each of the PoE devices controlling a plurality of ports.